Railway systems are known having a direct current catenary connected to a block of rectifier bridges that is in turn connected to the secondary winding of a transformer placed at the connection to the corresponding substation, the primary winding of which being connected to a three-phase alternating current grid, connecting an energy harnessing device between the catenary and the secondary winding of the transformer, so that during braking of the trains a certain voltage is supplied to the grid to allow making use of this energy.
FIG. 12, corresponding to the state of the art, shows an arrangement existing in railway substations with DC catenary in which the catenary 20 is fed through uncontrolled rectifier bridges 40 that do not allow energy flow from said catenary 20 to the AC grid 10, so that the railway unit or train, when braking, limits the voltage in the catenary 20 and the excess energy is burnt in a system installed for this purpose in the railway unit itself.
Improving on the situation described in the preceding paragraph, solutions have been proposed such as that shown in FIG. 13, also corresponding to the state of the art, allowing to recover energy by means of a device 60a, which however has drawbacks in that it can only recover energy when the voltage in the catenary 20 is high enough for the corresponding inverter circuit to regulate the current delivered to the grid 10. This solution, shown in FIG. 12, is not satisfactory because not all the energy available is used in the catenary 20 and because the quality of the current delivered to the grid 10 can be reduced by a lack of sufficient voltage.
Another solution of the state of the art is shown in FIG. 14, where the corresponding device 60b uses an independent transformer 70 to raise the voltage. In this case drawbacks appear related to the fact that the inversion and the installation volume are greater, and even so the system is subject to voltage fluctuations in the grid 10, without the working voltage being sufficient to optimize the quality of the current delivered.